This invention relates to temperature sensors and more particularly to sensors for determining the temperature of an open liquid body without making actual contact with that body. This invention is advantageously employed in conjunction with microscope slide staining apparatus of the type wherein a reagent film disposed on the surface of the slide must be maintained at a temperature within a predetermined range for a predetermined period of time to achieve optimal optical density and contrast.
In the microscopic examination of certain material, particularly cellular materials such as blood, tissue, or the like, a specimen of the material is placed on a transparent microscope slide. Thereafter, the material is stained by contacting it with solutions which stain or dye only certain constituents of the cell to provide a contrast which facilitates examination. Mechanized means are being increasingly employed for staining microscope slides. This type of apparatus conveys the slides through a plurality of stations where the staining reagents are automatically applied to the specimen. One such automatic staining apparatus is disclosed in U.S. Pat. No. 3,853,092 issued to L. G. Amos et al. This apparatus conveys the microscope slides in a circular path and automatically dispenses a metered amount of various reagents on the upper surface of the slides. The apparatus also imparts a nutating motion to the slide to effect uniform wetting of the top surface thereof by each reagent and by the rinse. The slides are thereafter moved to a near vertical position for draining and drying.
By controlling the time during which the specimen is subjected to each reagent and by carefully metering the amount of reagents applied, it is possible to obtain stained specimens exhibiting sufficient contrast for visual analysis. For example, laboratory technicians can perform what is referred to as a white blood cell differential by counting the leukocytes on a stained blood smear. Because of the amount of time required for a technician to analyze a biological specimen and due to the increasing number of analyses being performed, automation of tests such as the white blood cell differential is inevitable. A thesis by J. W. Bacus, "An Automated Classification of the Peripheral Leukocytes by Means of Digital Image Processing", University of Illinois, Chicago, 1971, describes one automated system. A system for automatically scanning and digitizing the count of leukocytes on a stained smear is disclosed in copending application Ser. No. 353,004 entitled "Image Scanning Converter for Automated Slide Analyzer" filed by D. A. Cotter on Apr. 20, 1973, now U.S. Pat. No. 3,883,852.
The accuracy with which automated slide analysis can be performed depends upon the reproducibility of the slide staining process. Each blood film, for example, should be stained so that the optical density of a given type of nucleus substantially achieves a specified value. Furthermore, the staining process should provide optimal contrast between the cell nucleus and cytoplasm. Apparatus capable of improving the reproducibility of the slide staining process is disclosed in U.S. Patent Application Ser No. 597,442 entitled "Microscope Slide Staining Apparatus Having Temperature Control" filed by C. H. Rogers et al. on even date herewith. The apparatus of that application comprises means for forming a film of staining reagents on the surface of a slide and heating means for flowing heated air over the surface of the reagent film. To maintain the film temperature within a predetermined range, a temperature sensor is employed to measure the temperature of the atmosphere surrounding the reagent film, and the sensor output controls the heating means. However, the film temperature is determined by a balance of the heating effect of the warm air and the cooling effect of evaporation from the film surface. The magnitude of this cooling effect is a strong function of ambient relative humidity; consequently, the film temperature cannot be regulated to the desired extent by simply holding the warm air temperature constant.